The present invention relates to a technology for improving exhaust emission of a hybrid vehicle that is driven by selectively utilizing an internal combustion engine and an auxiliary power source.
In recent years, internal combustion engines mounted in automobiles and the like are required to discharge the exhaust into the air after sufficiently removing harmful gas components such as carbon monoxide (CO), nitrogen oxide (NOx) and hydrocarbon (HC) that are contained in the exhaust. To satisfy the aforementioned requirement, there has been a well known technology of providing, in an exhaust passage of the internal combustion engine, an exhaust-purifying catalyst for removing the harmful gas components contained in the exhaust.
For example, such an exhaust-purifying catalyst includes a three-way catalyst that is formed by coating a surface of a ceramic carrier with alumina and carrying a platinum-rhodium-based precious metal catalytic substance on the alumina surface.
When the exhaust introduced into the three-way catalyst has an air-fuel ratio close to the stoichiometric air-fuel ratio, the three-way catalyst reacts hydrocarbon (HC) and carbon monoxide (CO) contained in the exhaust with oxygen (O2) therein, thereby oxidizing hydrocarbon (HC) and carbon monoxide (CO) into water (H2O) and carbon dioxide (CO2). At the same time, the three-way catalyst reacts nitrogen oxide (NOx) contained in the exhaust with hydrocarbon (HC) and carbon monoxide (CO) therein, thereby reducing nitrogen oxide (NOx) into water (H2O), carbon dioxide (CO2) and nitrogen (N2).
Such a three-way catalyst provided in the exhaust passage of the internal combustion engine removes carbon monoxide (CO), nitrogen oxide (NOx) and hydrocarbon (HC) contained in the exhaust of the internal combustion engine. Therefore, such harmful gas components can be suppressed from being discharged into the air.
The three-way catalyst is active at a predetermined active temperature (e.g., 300xc2x0 C. to 500xc2x0 C.) or higher. Therefore, if the temperature of the three-way catalyst is less than the predetermined temperature such as upon cold-starting of the internal combustion engine, the harmful gas components in the exhaust cannot be sufficiently removed.
In view of the foregoing problem, Japanese Laid-Open Patent Publication No. 10-236147 has proposed a regenerative catalytic apparatus. The regenerative catalytic apparatus described therein includes a honeycomb catalytic body provided within a heat-insulating container, a plurality of cylindrical heat-storage containers disposed in parallel within the catalytic body along the exhaust-flowing direction, and a heat-storage material provided in each cylindrical heat-storage container. While the internal combustion engine is in the operating state, the heat of the exhaust is stored in the heat-storage material. After the internal combustion engine is stopped, decrease in the temperature of the catalytic body is suppressed by utilizing the heat-insulation effect of the heat-insulating container and the heat stored in the heat-storage material. Thus, the catalytic body is activated early in the next starting of the engine.
In such a regenerative catalytic apparatus, the amount of heat stored in the heat-storage material depends on the operating state of the internal combustion engine. The operating state of the internal combustion engine in turn depends on the running conditions of the vehicle. Therefore, the amount of heat stored in the heat-storage material depends on the running conditions of the vehicle. Accordingly, the heat-storage material has not necessarily stored a specific amount of heat or more at the time the internal combustion engine is stopped. As a result, it may be difficult to retain the catalytic body at a specific temperature or higher until the engine is started subsequently.
In recent years, in order to reduce the fuel consumption, the amount of exhaust emission, or noise of the internal combustion engines mounted in the automobiles and the like, a hybrid vehicle has been developed, which includes two driving sources, i.e., an internal combustion engine and an electric motor, and which is driven by selectively operating the internal combustion engine and the electric motor.
In such a hybrid vehicle as well, it is important to remove harmful gas components contained in the exhaust emitted from the internal combustion engine before the exhaust is discharged into the air.
It is an object of the present invention to improve exhaust emission of a hybrid vehicle by providing a technology of achieving effective functioning of a regenerative catalytic apparatus by utilizing a feature of the hybrid vehicle of being driven by selectively operating an internal combustion engine and an auxiliary power source.
In order to achieve the object, a regenerative catalytic apparatus in a hybrid vehicle according to the present invention is provided with a hybrid mechanism for driving the vehicle by selectively operating an internal combustion engine and an auxiliary power source; an exhaust-purifying catalyst provided in an exhaust passage of the internal combustion engine for purifying exhaust flowing in the exhaust passage; and heat-storage means for storing heat generated in the internal combustion engine while the internal combustion engine is in an operating state, and utilizing the stored heat to suppress decrease in the temperature of the exhaust-purifying catalyst after the internal combustion engine is stopped.
In such a regenerative catalytic apparatus in the hybrid vehicle, the hybrid mechanism drives the vehicle only by an output of the auxiliary power source, only by an output of the internal combustion engine, or by both outputs of the internal combustion engine and the auxiliary power source, as required.
For example, when the amount of heat stored in the heat-storage means is less than a desired amount, the hybrid mechanism drives the vehicle by mainly utilizing the output of the auxiliary power source, as well as controls the operating state of the internal combustion engine so as to increase the amount of heat in the heat-storage means.
In this case, since the hybrid vehicle is driven mainly by the output of the auxiliary power source, the vehicle runs independently of the operating state of the internal combustion engine. On the other hand, the operating state of the internal combustion engine is controlled merely in order to increase the amount of heat in the heat-storage means, regardless of the running conditions of the hybrid vehicle. As a result, the heat-storage means can always store the desired amount of heat or more, irrespective of running conditions of the hybrid vehicle.
Consequently, the heat-storage means stores the desired amount of heat or more whenever the internal combustion engine is stopped. Therefore, decrease in the temperature of the exhaust-purifying catalyst can be reliably suppressed after the internal combustion engine is stopped. Thus, the exhaust emission at re-start of the internal combustion engine can be improved, as well as the fuel consumption for warming up the exhaust-purifying catalyst can be reduced.
A regenerative catalytic apparatus in a hybrid vehicle according to the present invention may be provided with a hybrid mechanism for driving the vehicle by selectively operating an internal combustion engine and an auxiliary power source; an exhaust-purifying catalyst provided in an exhaust passage of the internal combustion engine for purifying exhaust flowing in the exhaust passage; heat-storage means for storing heat generated in the internal combustion engine while the internal combustion engine is in an operating state, and utilizing the stored heat to suppress decrease in the temperature of the exhaust-purifying catalyst after the internal combustion engine is stopped; and engine control means for controlling the operating state of the internal combustion engine through the hybrid mechanism so that the amount of heat stored in the heat-storage means becomes equal to or more than a predetermined amount.
In such a regenerative catalytic apparatus in the hybrid vehicle, when the amount of heat stored in the heat-storage means is less than the predetermined amount, the engine control means controls the operating state of the internal combustion engine through the hybrid mechanism so that the heat generated in the internal combustion engine is stored in the heat-storage means.
At this time, the hybrid mechanism drives the vehicle by mainly utilizing an output of the auxiliary power source. More specifically, the hybrid mechanism controls the operating state of the internal combustion engine according to a request from the engine control means, as well as controls the auxiliary power source so as to satisfy the running conditions of the vehicle.
In this case, the hybrid vehicle is driven mainly by the output of the auxiliary power source independently of the operating state of the internal combustion engine. In other words, the operating state of the internal combustion engine is controlled merely in order to store the heat in the heat-storage means irrespective of the running conditions of the vehicle. As a result, the heat-storage means always stores the predetermined amount of heat or more, regardless of the running conditions of the vehicle. Thus, the heat-storage means stores the predetermined amount of heat or more at the time the internal combustion engine is stopped. Consequently, after the internal combustion engine is stopped, decrease in the temperature of the exhaust-purifying catalyst is prevented by the predetermined amount of heat or more stored in the heat-storage means.
The regenerative catalytic apparatus in the hybrid vehicle according to the present invention may further include temperature-detecting means for detecting a temperature of the heat-storage means. In this case, the engine control means may determine the amount of heat stored in the heat-storage means by using a detection value of the temperature-detecting means as a parameter. More specifically, the engine control means may determine that the amount of heat stored in the heat-storage means is the predetermined amount or more when the detection value of the temperature-detecting means is a predetermined value or more, and may determine that the amount of heat stored in the heat-storage means is less than the predetermined amount when the detection value of the temperature-detecting means is less than the predetermined value.
The engine control means may control the operating state of the internal combustion engine so as to increase the amount of heat generated in the internal combustion engine, when the detection value of the temperature-detecting means is less than the predetermined value. Moreover, the engine control means may control the operating state of the internal combustion engine into a normal operating state, when the detection value of the temperature-detecting means is the predetermined value or more. Further, the engine control means may be adapted to inhibit the stopping of operation of the internal combustion engine when the internal combustion engine is in the operating state and the detection value of the temperature-detecting means is less than the predetermined value, and to allow the stopping of operation of the internal combustion engine when the detection value of the temperature-detecting means is the predetermined value or more.
The heat-storage means according to the present invention may include a heat-storage material for storing heat of the exhaust emitted from the internal combustion engine. In this case, the engine control means may control the operating state of the internal combustion engine so as to increase the temperature of the exhaust emitted from the internal combustion engine, when the detection value of the temperature-detecting means is less than the predetermined value.
For example, the exhaust temperature of the internal combustion engine can be increased by retarding the ignition timing, increasing a fuel injection quantity and an intake-air quantity, or the like. Note that, in the case where the internal combustion engine is provided with a variable valve mechanism capable of varying the opening/closing timing of an exhaust valve, the exhaust temperature of the internal combustion engine may be increased by advancing the opening timing of the exhaust valve.